The present invention relates to a radiation detection method and apparatus, and more particularly, a radiation detection method and apparatus which compares binary digital data that has been stored in and retrieved from a radiation sensitive memory device and a radiation hardened memory device to detect radiation exposure.
Nuclear radiation, in sufficient quantities, is harmful to humans because it can destroy the genetic blueprint of our living cells. Such destruction can kill living cells, or can cause cells to mutate and multiply uncontrollably causing a cancer. There are three principal types of radiation: (1) charged particles such as alpha particles and beta particles; (2) uncharged particles or neutrons; and (3) photons or gamma rays which are emitted from nuclear reactors and the sun and stars. Exposure to minimal levels of radiation is largely unavoidable because radiation occurs naturally within the earth, traces of radioactive elements can make their way into our bodies, and inescapable cosmic rays from the sun and stars frequently strike the earth. However, some naturally occurring deposits and man-made radiation sources can cause harmful radiation exposure that should and can be avoided.
The U.S. Nuclear Regulatory Commission issues Federal Regulations defining levels of safe nuclear radiation. See Title 10 of the Code of Federal Regulations, Part 20 entitled xe2x80x9cStandards for Protection against Radiation.xe2x80x9d In these standards, a unit of radiation absorbed dose is the rad which equals 0.01 Joule/kilogram. One rad is required to deposit 100 ergs/gram in any material by any kind of radiation.
Radiation can be harmful to biological organisms including humans. Radiation with sufficient energy to produce ions (ionizing radiation) is more damaging to humans than non-ionizing radiation. As such, exposure tolerance values for humans have been developed in terms of a rem which is a dose equivalent unit. The conversion factor from rad to rem is the RBE (relative biological effectiveness). Rem equals the product of RBE times rad where RBE varies from 1 for X-rays and gamma rays to 20 for 1 Mev alpha particles.
More particularly, the Exposure Tolerance Values for Humans (Whole-body radiation dose) is as follows along with explanatory comments:
In order to detect radiation, radiation detection devices must be utilized since radiation cannot be sensed by sight, smell, or taste. A commonly known radiation detector is the Geiger counter. It was first built by Hans Geiger around 1911. This device measures the conductivity in a gas filled vacuum tube called the Geiger-Mueller tube. The tube""s conductivity increases with each radiation particle or high energy ray incident to the tube. The device""s electronics count the number of conductive pulses incident upon the tube per unit time as a measure of the radiation level. Unfortunately, this device is relatively large and expensive since much equipment is required to manufacture the tube and a high voltage power supply, such as 800 to 1000 volts, is required to operate the tube. Thus, this radiation detection device is not practical for the average consumer, cannot be easily transported, and is relatively expensive.
Another common radiation detection device is a scintillation detector. This device employs a radiation sensitive material, such as a sodium iodide crystal, along with a photo-multiplier tube amplifier (PMT). The radiation sensitive material converts radiation into photons which are multiplied into a measurable current by the PMT. This device is also relatively large and expensive, and is therefore impractical for the average consumer. As such, affordable radiation detection devices are not generally available that can be conveniently carried by a person in order to warn the person of exposure to unsafe radiation levels.
The above needs are met and other advantages are achieved by the present invention, which provides a method and apparatus for detecting radiation based upon a comparison of digital data that is stored in both a radiation sensitive memory device and a radiation hardened memory device. As a result of its design, the radiation detection method and apparatus is relatively inexpensive and is sized so as to be conveniently carried throughout the day in order to provide immediate warning of radiation exposure.
According to the present invention, the radiation detector comprises a digital data generator for producing digital data. Preferably, the digital data generator is a pseudo-random generator, such as a pseudo-random word generator that produces pseudo-random words. This radiation detector also comprises a radiation sensitive memory device for storing at least a portion of the digital data produced by the digital data generator for a test period during which time the digital data may be susceptible to radiation, and thereafter producing an exposed digital data stream. The radiation detector further comprises a radiation hardened memory device for also storing at least a portion of the digital data produced by the digital data generator, and for producing a test digital data stream which is synchronized to the exposed digital data stream produced by the radiation sensitive memory device. As its name suggests, the radiation hardened memory device is much less sensitive to radiation than the radiation sensitive memory device. Nevertheless, both the radiation hardened memory device and the radiation sensitive memory device can be shift registers through which digital data is clocked or shifted. In one advantageous embodiment, the radiation sensitive memory device and the radiation hardened memory device store a pseudo-random word produced by the pseudo-random word generator. Further, the radiation detector includes a comparator for comparing the exposed digital data stream with the test digital data stream to determine any differences there between. Preferably, the radiation detector also includes a bit error rate counter for measuring a bit error rate between the exposed digital data stream and the test digital data stream based on the differences noted by the comparator.
The radiation detector can also include a controller that receives the bit error rate and processes the bit error rate into a radiation exposure measurement. The radiation detector may also have a display for displaying the radiation exposure measurement. Further, the radiation detector may include an alarm which activates when the radiation exposure measurement exceeds a pre-set radiation exposure measurement threshold. In addition, the radiation detector may further comprise a clock for controlling a rate at which the various components, including the digital data generator, the comparator and the bit error rate counter, operate.
The invention also encompasses a method for measuring radiation. The method of this embodiment for measuring radiation comprises the step of generating digital data, such as pseudo-random digital words. This method further comprises the step of storing at least a portion of the digital data in a radiation sensitive memory device for a test period during which time the digital data may be susceptible to radiation, and thereafter producing an exposed digital data stream. Also, this method encompasses the step of concurrently storing at least a portion of the digital data in a radiation hardened memory device and thereafter producing a test digital data stream which is synchronized to the exposed digital data stream produced by the radiation sensitive memory device. In one embodiment, for example, at least a portion of the digital data is clocked or shifted through respective shift registers that comprise the radiation sensitive memory device and the radiation hardened memory device. In addition, a pseudo-random digital word can be stored in both the radiation sensitive memory device and the radiation hardened memory device which thereafter output an exposed word and a test word, respectively. This method also includes the step of comparing the exposed digital data stream and the test digital data stream to determine any differences there between.
The comparison of the exposed digital data stream to the test digital data stream preferably determines an error rate which is then processed to produce a radiation exposure measurement. If desired, the radiation exposure measurement can be displayed and/or an alarm can be activated if the radiation measurement reaches a pre-set radiation exposure measurement threshold, thereby warning of the potential for exposure to undesirably high levels of radiation. As a result of its design, however, the radiation detector method and apparatus is relatively inexpensive and is small enough to be conveniently carried throughout the day in a shirt pocket, on a belt loop or the like. Alternatively, the radiation detector can have a form factor like a wristwatch and can simply be worn on the wrist.